Oumuamua: Comet Or Interstellar Craft? It’s Leaving Our Solar System Too Quickly To Find Out

Michael Summers Professor of Planetary Science and Astronomy
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Our solar system is made up of a huge diversity of objects. There are the nine traditional planets, dozens of moons and dwarf planets, millions of asteroids, and trillions of comets, all bound by gravity to our sun. But in spite of that diversity, all of these objects share a common origin four and a half billion years ago when the sun and planets formed. That makes all of these objects a part of our solar system’s family.

But on Oct. 19, 2017 astronomers discovered something new. It was the first object found that did not share that common heritage. It was an object with a separate origin and was only briefly passing through our solar system. Astronomers gave it the name Oumuamua — in Hawaiian meaning “first visitor from far away” and it was indeed a visitor from the distant stars.

From its initial detection it was clear that Oumuamua was unusual. When first seen it had already made its closest approach to the sun and was moving away at a speed of around 200,000 miles per hour! It was moving so fast that astronomers had only a few months to study it before it was so far away as to be undetectable.

But during the brief time that it could be studied it became clear that Oumuamua was unique among all of the objects that astronomers have ever studied. Its shape was unlike anything else seen in our solar system. It was elongated, much like the shape of a cigar, roughly 400 meters long and 40 meters wide. And it didn’t appear to have a gas tail, as comets usually do when they approach the sun.

Oumuamua was rotating, or tumbling, in a way that suggested it had suffered a collision long ago. The fact that it had not broken apart due to that rotation meant that it must have a strong internal strength, much like rocky or metallic asteroids.

Astronomers have long believed that the interstellar medium would be populated with objects like comets and asteroids, debris left over from the formation of stars and planets. But its ease of detection suggests that the interstellar medium has thousands of times more debris than expected. Tens of thousands of such objects must be passing through our solar system as any given moment.

As Oumuamua moved away from the sun it appeared to accelerate outwards. This may seem bizarre, but comets are known to do this as our sun’s light evaporates ices on their surfaces that are facing the sun, and that rapid evaporation gives the comets a push outward. But the fact that no tail of gas or dust could be seen was intriguing. Nevertheless, this acceleration was ultimately used to classify Oumuamua as a comet.

Overall, the discovery of Oumuamua has given astronomers some surprising insights into the types of objects that populate the interstellar medium, and about the debris left over from star and planet formation. However, its bizarre nature left us with mysteries about its nature and origin.

The reputable Harvard astronomy Avi Loeb made a startling suggestion. He suggested that Oumuamua was so exotic that a possible intelligent origin should be considered. Its outward acceleration might indicate that it is a solar sail — a large microscopically thin sheet of material that would accelerate an object due to sunlight hitting it — much like a ship’s sail uses wind to move the ship along. Loeb suggested that Oumuamua might be a “broken” interstellar craft, with only the sail remaining. This would seem to suggest that the interstellar medium might be populated with relics of previous civilizations.

Loeb’s suggested cannot be ruled out. But such a conclusion would be so profound, and would radically change our view of humanity’s place in the universe, that it must be the conclusion of last resort.

So we are left with an intriguing mystery. What is it? We may never know. It is moving away so fast that it would be incredibly difficult to launch a spacecraft to catch it, and such a mission would have to begin soon. But whatever it is, we may not have to wait long to find more information. There should be more discovered in the next few years with improving telescopes and instrumentation.

Michael Summers is a professor of planetary science and astronomy at George Mason University.

The views and opinions expressed in this commentary are those of the author and do not reflect the official position of The Daily Caller.